This invention relates to an improved method and flask for producing a sand cake mold used in molten metal, flaskless sand casting procedures. By way of background, a well-known and widely used sand casting procedure involves the use of a flask which consists of a lower, drag frame section and an upper, cope frame section. The sections are packed with sand, around a pattern, to form a cavity into which molten metal is poured for solidification into a cast object.
Commonly, the cavity in the sand is formed by first positioning a solid, pattern half within the drag and then filling the drag with sand that is compacted around the pattern half. Next, the drag is inverted and the cope is mounted upon it. A cope pattern half is positioned inside of the flask, upon the drag pattern half, and the cope is filled with compacted sand. Then, the cope is removed from the drag, and the pattern is removed from both the cope and the drag to form the cavity. Repositioning the cope upon the drag forms the complete cavity into which the molten metal is to be poured.
During the time that the cavity is formed, suitable pouring passages or sprues, gates and risers are formed in the sand for the flow of metal into the cavity. Of course, more than one cavity may be formed at a time, depending upon the casting requirements, sizes, etc.
In this system of casting, after the metal solidifies, the cope and drag sections of the flask are removed, the sand is broken away from the solidified metal part and the cast metal part is complete.
In recent times, for production casting of large numbers of similar parts at increased volume and reduced labor, flaskless sand casting has been used. This involves, essentially, the same procedures as mentioned above, except that after the cavity is formed in the sand, within the flask, the sand "cake", i.e. the compacted sand block which contains the cavity and is located within the flask, is removed from the flask. The flask may be reused to form another sand "cake". Meanwhile, the flaskless cake proceeds to the casting area and molten metal is poured into it.
In many cases, the flaskless sand "cake" has sufficient structural integrity to receive molten metal and to permit solidification of the molten metal within it. In those cases where the hydrostatic pressures are too great for the flaskless sand "cake", a reinforcing jacket is positioned around the cake and a weighted cover plate may be placed upon the top of it to prevent the sand from breaking or to prevent the molten metal from bursting out through the sand.
In the flaskless type of operation, the flask and the pattern may be handled within an automatic machine which rapidly positions the cope and drag, fills and compacts the sand and permits removal of the completed sand cake rapidly, with minimal hand labor.
After the sand is compacted within the flask, the cope section may be opened and immediately removed. The cope may be opened by disconnecting some of the corners which make up the four sided cope frame by separating the frame walls at the corners. Thereafter, the sand cake may be pushed downwardly through the drag or, conversely, the drag pulled upwardly over the cake. Because the sand is compacted within the drag frame, it frequently is damaged in the separation of the drag from the cake due to the frictional drag and the sticking of the sand to the walls. However, it has been believed to be necessary to leave the drag in place around the bottom of the cake while the cope is removed, in order to protect the integrity of the cake and to prevent its damage during the removal of the cope. Hence, little has been done to prevent the drag-caused damage in the past.
Thus, the invention herein contemplates loosening or separating the drag from the sand cake before the cake is removed from the drag and also, a simplified system for loosening the drag. Moreover, the invention contemplates compacting the sand within the flask to a much greater degree than has been done in the past so that the cake is much harder or denser than prior cakes. This is possible because of the improved drag arrangement.